Pressure regulating valves are used, for example, in the breather line between crankcase and the intake manifold of an internal combustion engine. This involves not allowing the pressure or vacuum in the receptacles to be vented to increase beyond a predetermined value.
In internal combustion engines, blow-by gases occur that are produced by combustion gases in the cylinder getting past the cylinder piston into the crankcase. These blow-by gases allow the pressure in the crankcase to rise, whereby leaks and spillages of oil can be the result. In order to prevent a pressure increase and to discharge these blow-by gases in an environmentally friendly manner, these are conducted from the crankcase back into the air feeder line of the internal combustion engine. Furthermore, the specified negative pressure value should not be significantly undershot, because otherwise undesired air can be erroneously sucked into the crankcase.
In the pressure regulating valves that are currently being used, an element familiar to a person skilled in the art under the term “switching membrane” made from elastomer, commonly fluorosilicone rubber is generally employed. These switching membranes are very flexible because of the specific properties of elastomers. Depending on the applied pressure ratios, this switching membrane opens or closes an opening in the pressure regulating valve. The pressure ratio generally results from the pressure differential between the applied pressure in a first chamber and the pressure prevailing in a second chamber of the pressure regulating valve. The pressure in the first chamber may for example be the same as the atmospheric pressure. The switching membrane must react to low switching pressures on the order of 1 to 250 mbar.
Blow-by gases in an internal combustion engine are made up of unburned fuel components, motor oil components and other pollutants resulting from the combustion. These gases attack many elastomer types, whereby damages to the material properties can occur. The components made from these materials become brittle, porous and cracked. If the switching films are damaged, the environmentally damaging blow-by gases pass directly into the environment, because the system is no longer sealed. The switching membrane made from elastomer is generally executed as roll film, in order to realize a specific stroke of the switching membrane. The material in the roll region is also mechanically damaged through the unrolling motion by simultaneous contact with blow-by gases and can thus be damaged.
The DE 26 29 621 A1 discloses a diaphragm valve having a switching membrane that is designed as a switching film clamped at its edge between the housing and the housing cover which is to be brought into a sealing contact by a pressure member against a seating surface provided in the housing, wherein the switching membrane is made of a thinner layer of low elasticity, for example from PTFE, facing towards the housing interior that is resistant to aggressive through-flow media, and an additional, thicker layer made of elastomeric material. Diaphragm valves of this type are primarily used where a high chemical resistance of the materials coming into contact with the through-flow medium is required. Because elastomeric materials do not meet this requirement but the chemically resistant materials such as PTFE do not possess the elasticity necessary for a proper function, films comprising two layers are used. The contact pressure that is applied by the pressure member via the thick, rubber-like layer is transmitted as evenly as possible onto the sealing surface of the switching film that works together with the seating surface in the housing. In this arrangement, relatively large switching pressures of several bar are exerted on the switching membrane for closing the two-layered switching membrane via a pressure spindle that is connected to a hand wheel in order to ensure the necessary sealing function by the stiff PTFE layer.